Jacquard looms are used in order to take the warp threads in a weaving loom to the correct position so as to produce, in combination with the weft threads, the desired weave structure with a desired pattern. This is the case for flat weaving looms wherein warp threads are taken to the correct position before the weft is introduced in order to form the desired weave structure and figure, together with the weft threads. This is also the case with face-to-face weaving looms, wherein pile-warp threads and/or ground warp threads are taken to the correct position before the weft is introduced, so that the pile-warp threads and/or ground warp threads can form the desired figure and weave structure with the weft threads.
Such a jacquard loom comprises at least two rows of hooks and at least two knives, each of which continually moves up and down in counterphase opposite a row of hooks and each of which can take along or not take along the hooks of said row. Whether or not the hooks are taken along is controlled by so-called selection elements which retain the hooks during one or several cycles when the hooks of the jacquard loom are in the top or bottom position (depending on the design). Two hooks, which are connected to each other by means of an upper hoisting cord which is passed around a hoisting wheel and each of which is moved by a knife, in which case the two respective knives move in counterphase, form a complementary hook pair. Often, these hooks are situated exactly opposite each other and the same selection element controls whether or not they are taken along by the knives. However, these hooks may also be influenced by various selection elements.
When they are optionally selected or not selected, hooks of one or two complementary hook pairs assume different positions. By assuming these different positions, by a cooperation between these hooks and the hoisting wheels of hoists and reversing rollers which is imposed by the mutual connection, by the upper hoisting cords and lower hoisting cords which are turned over these hoisting wheels and, if desired, over reversing rollers, and by connecting these hoisting cords, via harness cords, to one or more heddles which are provided with an opening through which a warp thread passes, these cooperating hooks take the associated warp threads to the desired height in order to produce a fabric with a well-defined pattern. The upper hoisting cord connects the ends of two complementary hooks. The lower hoisting cord is connected to the harness cord.
At its one end which is connected to one or more heddles via one or more harness cords, the lower hoisting cord is subjected to a tensile force exerted by springs which are connected to the heddle(s), and at its other end may be held in a fixed point of the module or to another part of the jacquard device which determines the position of the end.
A jacquard device may additionally be provided with setting means which enable setting of a number of lower hoisting cords per group, so that their reciprocating movement takes place at a different height. This makes it possible, for example, to place a group of yarns which is moved by this group of lower hoisting cords in a different layer, in their end position, than the yarns of another group.
By means of these setting means, it is not only possible to adjust the height of the heddle eyelets of the jacquard heddles attached to the harness cords without having to adjust the height of the entire jacquard loom, but they also provide an additional facility for control.
The jacquard looms are constructed to be as compact as possible in order to fit as many hooks and associated selection elements and hoist systems as possible on a specific surface area. The selection elements are becoming increasingly smaller and the hoist systems have to follow this trend for miniaturization. A hoisting device requires regular maintenance and checks, for example to replace defective or worn or ruptured hoisting cords or hoists. Thus, an operative has to work his way through the other hoists and hoisting cords in order to replace the defective or worn hoist or cord.
However, replacing or repairing hoisting cords when they are ruptured or worn is time-consuming.
In order to limit the downtime of the jacquard during rupture or during maintenance work, specific modules have been developed incorporating the different components of the hoist system.
Such a module in which the movable shed-forming means, the selection devices and the hoisting device of several shed-forming mechanisms are combined, is described in European patent publication EP 0 214 075. However, this known module has the following drawbacks: if one or more selection devices have to be repaired or replaced or have to be removed for maintenance, the harness cords which cooperate with the hoisting devices provided in the module have to be unhooked before the module can be removed. After a module has been put back in place, these harness cords have to be hooked back in. Having to unhook and hook the harness cords back in is laborious and time-consuming.
Furthermore, when such a module is replaced due to rupture or wear of one or more hoisting cords, the intact and expensive selection devices which are fitted in the same module are also replaced.
In order to solve, inter alia, the abovementioned problems, the European patent publication EP 0 801 161 describes a shed-forming device which comprises a separately removable selection module containing the selection elements and a separately removable hoisting module containing the hoists and the shed-forming means (hooks).
However, both modular solutions (the one from EP 0 214 075 in FIGS. 6 and 7, and the one from EP 0 801 161) suffer from the drawback that the tensile force of the springs is transferred completely to the module itself and that, during normal operation of the jacquard device, a force which is to be prevented is exerted in the direction in which the module is removed, namely in the direction in which the knives move and away from the heddles; in a normal embodiment, this will be mainly vertically upwards. This has the drawback that the module is subjected to unnecessary loads, which may result in deformation which is disadvantageous with regard to the good guidance of the components which are situated therein.
In addition, an additional provision has to be made to prevent the module from sliding upwards during operation of the jacquard device, for example in the form of additional clamping or connecting elements.